The long-term objective of this proposal is to elucidate the androgen action pathway, a cascade of molecular and cellular events triggered by androgen manipulation leading to cell proliferation, differentiation, and/or apoptosis in the prostate. In the past grant period (1996-2000), we have identified and characterized 25 genes that are up-regulated by androgen and 4 genes that are down-regulated by androgen during the initial regrowth of the castrated rat ventral prostate. One of the up-regulated novel genes, U 19, encodes a conserved protel. U 19 expression is restricted to the urogenital tract during embryonic development and in adult animals. U19 overexpression in prostate cancer cell lines markedly inhibits cell proliferation in culture, suggesting that U19 encodes a novel protein that regulates cell proliferation. Ectopic expression of U19 in the epithelial cells of the ventral prostate in the transgenic mice appears to significantly increase (2-3 fold) the number of the epithelial cells per unit area and to alter the regional heterogeneity of the prostate ductal system, suggesting that U 19 plays an important role in cellular differentiation and proliferation in vivo. These observations support our hypothesisthat the in vivorole of U19 is dedicated to the regulation of androgendenendent cell proliferation and differentiation in the prostate and the other male sex accessory organs. Four specific aims are proposed to define the role of U 19. 1. Determine the functional domains of the U 19 gene product critical in the inhibition of cell proliferation. U19 deletion and substitution mutants will be generated to map domains and motifs essential for inhibiting proliferation of prostate cancer cells. 2. Characterize the expression and intracellular localization of the U19 protein in the prostate. U19 expression during the development of male sex accessory organs and its response to androgen manipulation will be studied in mice at both mRNA and protein levels using in situhybridization, immunohistochemistry, Northern blot, and Western blot. Intracellular localization of the U19 protein will also be determined by immunofluorescence microscopy. 3. Determine the effect of U19 overexpression on the prostate. The effect of U19 overexpression on the prostate during growth and androgen manipulation will be examined in U 19 transgenic mice. 4. Determine the effect of U19 gene deletion on the prostate. The impact of U19 gene deletion on the prostate during development, aging,and androgen manipulation will be analyzed in U 19 geneknockout mice.